An Evaluation of Loading Systems

Telephone subscriber-line plant consists largely of cable pairs which, for lengths in excess of 18 kilofeet (kf) (18 000 feet), require loading to provide acceptable transmission. Various loading systems have been used over the years to secure optimum transmission with the telephone instruments representing the state of the art at the time. The current trend in exchange plant is to place even the longest rural telephone circuits in buried cable. This implies the application of loading, together with a judicious control of bridged taps beyond the last loading coil. Tests were therefore made on 24-gauge, 22-gauge, and 19-gauge artificial cable pairs loaded to the H-88, D-88, and D-66 systems described herein with varying lengths of bridged tap and using variously weighted noise as a test signal, and variously weighted "detectors." In this paper the test results are evaluated to show the relative "advantages" of the D-66, D-88, and H-88 loading schemes.